Optical networks, such as for example, distributed Wavelength Switched Optical Networks (WSONs) support end-to-end optical paths, called lightpaths, between nodes requiring connection in the network. Intermediate nodes in this type of network support wavelength switching and may also support wavelength conversion. Establishing routes over such a network is constrained by the availability of wavelengths. This is typically addressed by resorting to the Label Set (LS) Generalized Multi-Protocol Label Switching (GMPLS) object, which collects wavelength availability information during the signalling phase of the lightpath setup process. The recent availability of flexible optical cross-connects prototypes is driving the introduction of flexible grids, i.e. frequency slots of reduced width (e.g., 6.25 GHz or 12.5 GHz) which need to be reserved in a contiguous way according to the number of frequency slots required by the lightpath.
In flexible grid network scenarios, traditional wavelength assignment strategies have been established. One such known strategy is known as “first-fit”. This wavelength assignment strategy assigns a first available frequency slot for a data transmission or at least a first available contiguous number of required slots for data transmission. However, such a strategy may not guarantee efficient network resource utilization because of the different granularity of the requests.
Moreover, the evolution of the GMPLS protocol to cope with frequency slots rather than wavelengths is not straightforward since it may determine scalability problems. For instance, regarding Resource Reservation Protocol-Traffic Engineering (RSVP-TE) signalling protocol, while the typical size of LS refers to 40 or 80 wavelengths, in flexible grid scenarios, the number of frequency slots is significantly high, e.g. 320 or 640 with slot widths of 12.5 or 6.25 GHz respectively.